Turn ON and OFF method of SCR or thyristor and natural communication & commutation method

Turn ON and Off method of thyristor:- 

Thyristor 

Turn ON method of thyristor:-

We can switch ON means the thyristor switched non constructing state to conducting stage by many methods. These several methods are given below:- 

Forward voltage triggering:- when anode to cathode voltage means forward voltage in increased with gate circuit open the reverse bias junction J2 will have an Avalanche breakdown voltage called break over voltage.Due to this voltage the thyristor change their state non conducting state to conducting state means OFF state to ON state.  During ON state voltage is 1 to 1.5 volt.

Thermal triggering:- In this method when we increase the junction temperature then thyristor decreases their width of depletion layer because it is made up of semiconductor type material. 

When voltage applied between anode and Cathode is very nearly to its breakdown voltage or Avalanche breakdown voltage then the device can be triggered by the increasing in the junction temperature. Due to increase in temperature the situation when the reverse bias junction collapse and making the device conducting this method is known as thermal triggering method or thermal triggering process.

Radiation triggering or light  triggering:- 

In this method the name shows the triggering method like when be trigger with the help of light the photon energy at that time hole pair is generated in the junction depleation layer at this instant time the current follow and the conduction between the device are on this process is known as radiation triggering and light triggering method. 

DV/DT triggering method:-In this method the device junction j1 and j3 forward bias and J2 is Reverse bias where they have a characteristic of capacitor due to charge across the junction if a forward voltage is suddenly applied at charging current the flow of current is conduct and the device will be triggered.

Gate triggering:-

Gate triggering is the most common method for triggering the SCR or thyristor by applying a positive voltage at the gate terminal at that time the flow of current is conduct and the thyristor is ON and start conduction. In GATE Terminal 3 type of signal are applied DC signal, AC signal or pulse signal.

Dc gate triggering:-
In dc triggering in DC voltage applied on gate becomes positive with respect to cathode when we applied a sufficient voltage they produce break over voltage and start conducting the device. 

Ac gate triggering:-
In AC Gate triggering a AC signal are triggered in the gate terminal AC signal change the phase angle and control the signal due to this system the SCR or device are Trigger.

Pulse gate triggering:-
In pulses Gate trading method an external pulse generator circuit are used for trigger an GATE terminal to ON the device or ,to conduct the device or to change the state.

Turn OFF method:- 

Anode current decreases.

Give bias voltage on gate terminal. 

Negative voltage supply at gate terminal. 

By two types of commutation method. 

1. Natural communication / line commutation :-In this method naturally ON/OFF SCR automatically,or naturally like ,phase angle change of AC voltage.
2. Forced commutation / load commutation :- In this method SCR OFF with the help of external circuit.